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CHAMBER AND METHOD FOR STERILIZATION TREATMENT AND MACHINE AND PROCESS FOR PRODUCING PACKAGES

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a chamber for sterilization treatment of an object of packaging material passing through the chamber, and a method for sterilization treatment of an object of packaging material. The invention also relates to a machine for producing packages comprising such a chamber, and a process for producing packages comprising such a method. The chamber comprises a device for determining a concentration of a sterilization agent in a gas mixture inside the chamber and means for maintaining a higher pressure inside the chamber than outside the chamber at an object exit opening thereof.

BACKGROUND ART

Within the food industry, beverages and other products are often packed in paper or paperboard based packages. Packages intended for liquid food are often produced from a packaging laminate comprising a core layer of paper or paperboard and an outer, liquid-tight layer of thermoplastic material on at least that side of the core layer which will form the inside of the packages. For particularly oxygen sensitive food products, such as fruit juice and cooking oil, the packaging laminate usually further comprises a layer of a gas barrier material. This layer is in most cases an aluminum foil which also enables induction sealing of the packaging laminate.

The packages are often produced in a packaging machine where a web of packaging laminate is formed into a tube which is closed by sealing of the longitu- dinal edges of the web in an overlapping condition. The longitudinally sealed tube is continuously filled with a product and then transversally sealed, wherein filled "cushions" are formed. The transverse sealing is made along narrow, transverse, mutually spaced apart, sealing zones. After the transverse sealing, the "cushions" are separated from the rest of the tube by incisions in the sealing zones and final- Iy formed into the desired shape.

Nowadays, also so-called carton bottles are frequently occurring packages. In substance, these are composed of a lower part in the form of a sleeve of packaging laminate like the one described above, and an upper part in the form of a plastic top provided with an opening device, such as a cap. The carton bottles are often produced in a packaging machine where sheets, so-called blanks, of packaging laminate are formed into tubes which are closed by sealing of two opposing edges of each sheet in an overlapping condition. Then, each tube is slipped over

a respective plastic top and arranged in such a way that a major part of the plastic top protrudes from the tube. After sealing of the top and the tube along a contact surface between them, the package is filled, sealed at the open end of the tube for achieving a sleeve and closing the package, and finally formed into the desired shape.

The manufacturing processes above are well known and will not be described in detail.

To extend the shelf life of the products packed, it is prior known to sterilize the packaging material prior to the filling operation and sometimes also the for- ming operation. Depending on the desired shelf life and whether the packages are to be distributed and stored in a chilled or ambient environment, different levels of sterilization can be chosen.

A known way of sterilizing packaging material is chemical sterilization. As an example, chemical sterilization can be made by passing the packaging material through a bath of hydrogen peroxide solution and then through a heating chamber. In the heating chamber, hot sterile air is introduced for heating the packaging material to such a degree that the hydrogen peroxide is evaporated and thus removed from the surface of the packaging material.

The above method works excellent when it comes to sterilization of a conti- nuous web of packaging laminate but is obviously less suited for sterilization of open carton bottles prior to filling.

In connection with carton bottles, so-called gas phase sterilization can instead be used. Such sterilization can be made by passing the carton bottles through a preheating chamber for preheating, a gassing chamber containing gaseous hydrogen peroxide and then through a venting chamber. In the venting chamber, the carton bottles are exposed to a flow of hot sterile air for removal of residues of hydrogen peroxide. A gas phase sterilization device adapted for sterilization of carton bottles is known from the Swedish patent number 0203692-9, which is hereby incorporated herein by reference. For proper sterilization of the packaging material, in the peroxide bath case, accurate control of the hydrogen peroxide concentration in the gas mixture inside the heating chamber is crucial. If the concentration is too low, the hydrogen peroxide applied onto the packaging material evaporates too quickly resulting in a risk of insufficient sterilization. On the other hand, if the concentration is too high, the hydrogen peroxide applied onto the packaging material evaporates too slowly resulting in a risk of unallowable peroxide residues on the packaging material leaving the heating chamber. Similarly, in the gas phase sterilization case, accurate control of the hydrogen peroxide concentration in the gas mixture inside the gas-

sing chamber is crucial. If the concentration is too low, there is a risk of insufficient sterilization. Further, if the concentration is too high, there is a risk of too much peroxide on the carton bottles leaving the gassing chamber and, consequently, a risk of unallowable peroxide residues on the carton bottles leaving the venting chamber. In either case, if the peroxide concentration is not within certain limits, the settings of the packaging machine should be changed.

There are many ways of determining a hydrogen peroxide concentration. In a known packaging machine with a hydrogen peroxide bath as described above, the hydrogen peroxide concentration in the gas mixture inside the heating cham- ber is estimated by the machine control system based on the concentration of hydrogen peroxide in the solution, the consumption of hydrogen peroxide solution and the air mass flow inside the heating chamber. Thus, here the hydrogen peroxide concentration is theoretically calculated from known external parameters. This is a somewhat uncertain determination method and it involves a risk of erroneous concentration determinations and, thus, a risk of false alarms, or the packaging material being insufficiently sterilized or too high levels of residual hydrogen peroxide being left on the packaging material.

In a known packaging machine with a gassing chamber as described above, the hydrogen peroxide concentration in the gas mixture inside the gassing cham- ber is measured by means of IR-sensors. However, such sensors are bulky, fragile and cost a lot of money.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a chamber for sterilization treatment of an object of packaging material passing through the chamber, a machine for producing packages comprising such a chamber, a method for sterilization treatment of an object of packaging material and a process for producing packages comprising such a method, which, at least partly, eliminate potential limitations of prior art. The basic concept of the invention is to provide an im- proved sterilization treatment solution with determination of sterilization agent concentration by direct temperature and pressure measurements in the actual sterilization environment. Such a direct determination is more precise than a theoretical calculation based on external parameters and gives more accurate results. In turn, this means a reduced risk of false alarms. Additionally, such a determination is advantageous compared to a determination by means of IR- sensors since equipment for measuring temperature and pressure can be made relatively durable and small. Also, such equipment is comparatively cheap.

The chamber, machine, method and process for achieving the object above are defined in the appended claims and discussed below.

A chamber for sterilization treatment of an object of packaging material passing through the chamber, according to the present invention, comprises a device for determining a concentration of a sterilization agent in a gas mixture inside the chamber and means for maintaining a higher pressure inside the chamber than outside the chamber at an object exit opening thereof. The chamber is characterized in that the device comprises a catalyst, an outlet of the catalyst being connected to an outside of the chamber and an inlet of the catalyst being connected to an inside of the chamber so that the higher pressure inside the chamber forces the gas mixture through the catalyst for decomposition of the sterilization agent, thermometers for measuring a temperature difference across the catalyst, a pressure sensor for measuring a first pressure inside the chamber and a second pressure outside the chamber, and processing means for determining, based on the temperature difference and a pressure difference between the first and the second pressure, the concentration of the sterilization agent in the gas mixture inside the chamber.

By sterilization is meant removal or killing of micro-organisms to a certain extent chosen in dependence of the specific application. Thus, as pointed out above, different levels of sterilization can be chosen depending on how the final packages are to be stored and distributed.

As used herein, sterilization treatment is a generic term for operations performed in connection with sterilization of an object, e.g., as described above, gassing for exposure to the sterilization agent and evaporation for removal of sterili- zation agent after exposure. Accordingly, the inventive chamber can be of different types, for example, a gassing chamber and/or a heating chamber, as described above.

By the chamber comprising a device for determining a concentration of a sterilization agent in a gas mixture inside the chamber, the sterilization treatment can be monitored so as to achieve the desired sterilization result.

Since the chamber comprises means for maintaining a higher pressure inside the chamber than outside the chamber, at an object exit opening thereof, it is possible to ensure that any passage of gas mixture through the catalyst occurs from the chamber to the surroundings and not the other way around, which is beneficial from a contamination point of view.

The catalyst can be of different types and made of different materials depending on the sterilization agent used. The position of the catalyst results in that the gas mixture inside the chamber automatically is driven there through,

which, in turn, means that no additional means, such as a pump or a fan, is required for this purpose.

When the gas mixture enters the catalyst, the sterilizing agent is preferably spontaneously decomposed into decomposition products which, naturally, are dependent upon the sterilization agent used. In connection therewith, heat is generated causing a temperature rise inside the catalyst. Thus, the temperature difference across the catalyst indicates the amount of sterilization agent decomposed. The percentage of the sterilizing agent that is entering the catalyst and that is decomposed therein is dependent upon different factors, such as the physical properties of, and the mass flow through, the catalyst, the latter, in turn, being dependent upon the pressure difference across the catalyst. Accordingly, the processing means of the chamber can use the temperature difference together with the pressure difference to calculate the concentration of sterilization agent inside the chamber in a direct and very neat way. According to one embodiment, the temperature means is arranged to measure a first temperature inside the chamber and a second temperature at the outlet of the catalyst. Here, the temperature difference is equal to a difference between the first and second temperatures. This embodiment is beneficial since the determination of the concentration of the sterilization agent becomes particu- larly neat and precise. The fact is that the decomposition degree at the outlet of the catalyst is at a maximum which normally corresponds to a maximum temperature. Further, at a state of equilibrium, the temperature is about the same essentially everywhere inside the chamber which means that the first temperature can be measured with essentially the same result at a large number of different locations inside the chamber.

The inventive chamber can be constructed in such a way that the catalyst at least partly is arranged inside the chamber. This is an advantage since it, under normal circumstances, is warmer inside the chamber than outside the chamber. By arranging the catalyst at least partly inside the chamber, the emission of heat generated inside the catalyst in connection with the sterilization agent decomposition is minimized. Obviously, this makes the determination of the sterilization agent concentration more accurate and simple.

Further, the chamber can be such that the higher pressure inside the chamber continuously forces the gas mixture through the object exit opening. This means that the gas mixture is leaving the chamber, not only through the catalyst, but also through the object exit opening. However, the sterilization agent in the gas mixture forced through the object exit opening is not decomposed before leaving the chamber.

As apparent form the above paragraphs, the gas mixture leaving the chamber through the catalyst may not be completely free from sterilization agent. Further, the gas mixture leaving the chamber through the object exit opening is certainly not free from sterilization agent. In view of this, the chamber can be so constructed that the gas mixture leaving the chamber is directed through a main catalyst for decomposition of the sterilization agent before being released. This is beneficial since it prevents discharge of sterilization agent out in the open.

According to one embodiment of the invention, the chamber further comprises means for removing, by heating, sterilization agent from the object of packa- ging material. The heating chamber described above in the section about background art is constructed in accordance with this embodiment.

Further, the construction of the chamber can be such that it is arranged to receive the object of packaging material after application of the sterilization agent. The heating chamber described above in the section about background art is constructed like this. The sterilization agent can be applied to the packaging material, for example, by passage through a bath, by condensing or by gassing.

The inventive chamber can be such that the catalyst is arranged inside a housing, such as a tube or a casing. Such a housing may serve as a protection for the catalyst which may be comparatively fragile. Further, the housing may be insulating for reducing emission of heat generated therein in connection with the decomposition of the sterilization agent. This is advantageous since it makes the determination of the sterilization agent concentration more accurate and simple. According to one embodiment of the invention, the chamber further comprises directing means for directing the object of packaging material, which is in the form of a continuous web, through the chamber. Thus, this embodiment relates to sterilization of the packaging material before forming of packages.

According to an alternative embodiment, the chamber further comprises conveying means for conveying the object of packaging material, which is in the form of a partly formed packaging container, through the chamber. One example of such a partly formed packaging container is the above described carton bottle open at one end.

The chamber can be used in connection with different types of sterilization agents. As an example, it can be adapted for sterilization with hydrogen peroxide, which is an effective, well-known and reliable sterilization agent. A machine for producing packages according to the present invention comprises a chamber for sterilization treatment of an object of packaging material passing through the chamber as described above.

A method for sterilization treatment of an object of packaging material, according to the present invention, comprises passing the object through a chamber, determining a concentration of a sterilization agent in a gas mixture inside the chamber and maintaining a higher pressure inside the chamber than outside the chamber at an object exit opening thereof. The method is characterized in further comprising providing a catalyst, an outlet of the catalyst being connected to an outside of the chamber and an inlet of the catalyst being connected to an inside of the chamber, forcing, by the higher pressure inside the chamber, the gas mixture through the catalyst for decomposition of the sterilization agent, measuring a temperature difference across the catalyst, measuring a first pressure inside the chamber and a second pressure outside the chamber, and determining, based on the temperature difference and a pressure difference between the first and the second pressure, the concentration of the sterilization agent in the gas mixture inside the chamber. A process for producing packages according to the present invention comprises a method for sterilization treatment of an object of packaging material as described above.

The characteristics discussed in connection with the inventive chamber are, of course, transferable to the inventive machine, method and process. Further, these characteristics may naturally be combined in the same embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail with reference to the appended schematic drawings, which show examples of presently non-limiting preferred embodiments of the invention.

Figure 1 is a cross-sectional view, with parts removed for clarity, of a machine for producing packages comprising a chamber according to a first embodiment of the present invention.

Figure 2 is a cross-sectional view, with parts removed for clarity, of a machine for producing packages comprising a chamber according to a second embodiment of the present invention.

Figure 3 is a cross-sectional view, with parts removed for clarity, of a machine for producing packages comprising a chamber according to a third embodiment of the present invention. Figure 4 is a cross-sectional view, with parts removed for clarity, of a machine for producing packages comprising a camber according to a fourth embodiment of the present invention.

Figure 5 is a cross-sectional view of a catalytic arrangement of the fourth embodiment of the present invention.

Figure 6 is an exploded view of the catalytic arrangement of the fourth embodiment in figure 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In figure 1 , a machine 10 working in accordance with a predetermined process for producing packages from a tube (not shown) of packaging laminate is shown. The packaging laminate is of the initially described kind, i.e. it comprises a paper core layer, an aluminum gas barrier layer and outer layers of thermoplastic material, and similar kinds of packaging material are also possible, e.g. with additional layers or without an aluminum layer. As initially described, the tube is formed by sealing of the longitudinal edges of a web 12 of packaging laminate in an overlapping condition. After forming, the tube is filled with the intended product and transversally sealed at regular intervals. The "cushions" thus formed are separated from the rest of the tube and finally formed into the desired shape. Continuous forming, filling and sealing of a tube like this is well-known and will not be described in detail herein.

Prior to tube forming, the web 12 of packaging laminate is sterilized. To this end, the web 12 is directed, by means of directing rollers 14 and 16, through a bath 18 containing a hydrogen peroxide solution. As an example, the bath can be of any of the types described in applicant's Chinese patent applications number 200510069635.8 and 200510133873.0, which are hereby incorporated herein by reference. After leaving the bath 18, the web 12 is passed between two squeegee rollers

20 for evenly spreading out the peroxide solution over the entire width of the web 12 and removing excess peroxide. Then, the web 12, now carrying droplets of hydrogen peroxide solution, is directed, by means of directing rollers 22, 24, through a heating chamber 26 for further hydrogen peroxide removal by evapora- tion. The web 12 enters the heating chamber 26 through an entrance opening 28 and exits the same through an exit opening 30.

The heating chamber 26 comprises a heating arrangement, schematically illustrated by the box with dashed lines and denoted 32 in figure 1 , for effecting the evaporation of the hydrogen peroxide solution applied onto the web 12. The heating arrangement 32, which, for example, can be of the type described in applicant's Chinese patent application number 200510069630.5, hereby incorporated herein by reference, is arranged to introduce hot sterile air into the heating chamber. By hot air is meant air of a temperature that is high enough to perform

the evaporation of the sterilization agent used, here hydrogen peroxide. Further, the heating arrangement 32 is arranged to maintain a higher pressure inside the heating chamber 26 then outside the same, with the exception of the compartment 21 above the bath just below the heating chamber 26. In this part of the bath, the part to the right of partition wall P in figure 1 , the pressure is essentially the same as inside the heating chamber, whereas there is essentially atmospheric pressure in the part of the bath to the left of partition wall P. After leaving the heating chamber 26, the web 12 passes an intermediate chamber 34 before the tube forming, filling and sealing takes place. The heating arrangement thus comprises means for supplying air to the heating chamber 26, such as a fan or similar (not shown).

In order to achieve a proper sterilization of the web 12, it is very important that the environment inside the heating chamber is carefully controlled. Specifically, it is essential to frequently measure the hydrogen peroxide concentration in the gas mixture inside the heating chamber 26, which gas mixture consists of air and gaseous hydrogen peroxide evaporated from the web of packaging laminate when passing through the heating chamber 26. The hydrogen peroxide concentration inside the heating chamber is dependent upon a number of different parameters, such as the hydrogen peroxide concentration in the solution in the bath 18, the consumption of the solution in the bath and the flow of hot sterile air into the chamber. If the hydrogen peroxide concentration inside the heating chamber is too high, there is a risk of unallowable residues of hydrogen peroxide on the web when this leaves the heating chamber. On the other hand, if the hydrogen peroxide concentration inside the heating chamber is too low, there is a risk that the web is inadequately sterilized when it leaves the chamber. If the hydrogen peroxide concentration is not within predetermined limits, the settings of the machine should preferably be adjusted.

In accordance therewith, the heating chamber 26 further has a device 36 for determining the concentration of hydrogen peroxide in the gas mixture inside the heating chamber 26. The device 36 comprises a housing 40 accommodating a measuring catalyst means or catalyst 38 in the form of a body of ceramic material dipped in precious metal solution, such as platinum solution. The catalytic body has the outer shape of a rectangular parallelepiped. Channels with essentially square-shaped cross-sections running side by side in the longitudinal direction of rectangular parallelepiped fill up the entire interior of the catalyst 38. This structure gives the catalyst 38 a lattice-like cross-section in the transverse directions. A circular cross-section or similar of the catalytic body is also possible, as well as channels therein having circular cross-sections or similar.

The catalyst 38 is surrounded by an insulating housing 40, e.g. made of a mixture of glass and Teflon®, foamed silicone or foamed Teflon® or similar, having poor heat conductivity both in the radial direction and the longitudinal direction of the housing 40. The inner dimensions of the housing correspond to the outer dimensions of the catalyst 38 so that the catalyst fills up essentially the whole housing in the transverse directions. The catalyst 38 and most of the insulating housing 40 are arranged inside the heating chamber 26 in such a way that an outlet 42 of the catalyst 38 is directly connected to the outside of the heating chamber 26, more particularly, the intermediate chamber 34, whereas an inlet 44 of the measuring catalyst means is directly connected to the inside of the heating chamber. The housing 40 is, in some embodiments, used for connecting the outlet 42 of the catalyst 38 to the intermediate chamber 34. The housing 40 can also be made from a metal, such as aluminium, stainless steel or similar, and be insulated on the inside with a separate insulating material, such as a mixture of glass and Teflon®, foamed silicone or foamed Teflon® or similar.

The higher pressure inside the heating chamber 26 forces the gas mixture of hydrogen peroxide and air through the exit opening 30 and through the housing 40, and thus also through the catalyst 38. Essentially no gas mixture leaves the heating chamber 26 through the entrance opening 28 because of the construction of the bath 18. When the gas mixture passes through the catalyst 38, the hydrogen peroxide is spontaneously decomposed into water and oxygen in an exothermic reaction according to the formula below:

H ₂ O ₂ (g) → H ₂ O(g)+l/2O ₂ (g) AH _Dec = 23 A4kcal/mol

Because of the arrangement of the catalyst 38 inside the insulating housing 40 and within the heating chamber 26, most of the heat generated is kept within the catalyst 38 resulting in a temperature rise therein. Assuming that the heat loss is zero, the temperature rise is proportional to how much hydrogen peroxide that is decomposed inside the catalyst, i.e.,

c _HA = k ₁ - δT + a , where a = 0.

All of the hydrogen peroxide entering the catalyst 38 is not necessarily decomposed therein. The decomposition of hydrogen peroxide in the catalyst 38, expressed as a percentage, is dependent on a number of different parameters, such as the mass flow through the catalyst 38 and the physical properties of the catalyst 38 as well as the insulating housing 40. For one and the same

equipment, a certain mass flow through the catalyst 38 results in a certain degree of hydrogen peroxide decomposition therein. Thus, there is a specific linear relationship between hydrogen peroxide concentration and temperature, i.e. a specific value of ki in the above equation, for each mass flow m . More particularly, experiments have shown that k-i is a linear function of the mass flow through the housing 40, i.e.

k _x = f{m), which yields c _HA = f(m)-AT .

Since m ~ the pressure drop across the insulating housing, the above formula can be rewritten as

The necessary form of the functions f(m) and g(δp) can be found by proper calibration of the sensor together with a reference means of measuring mass flow, pressure drop and hydrogen peroxide concentration. Such reference measuring means can e.g. be a mass flow meter, a calorimetric mass flow meter or similar accurate reference mass flow meter, and a UV concentration sensor or similar accurate concentration measurement means.

Thus, if the temperature rise in the catalyst 38 and the pressure drop across the insulating housing 40 are known, the concentration of hydrogen peroxide in the gas mixture inside the heating chamber 26 can be readily calculated. In accordance therewith, the device 36 further comprises thermometers 46 in the form of thermocouples for measuring a first temperature inside the housing 40 at the inlet 44 of the catalyst 38 and a second temperature inside the housing 40 at the outlet 42 of the catalyst, and a pressure sensor 48 in the form of a differential pressure gauge for measuring a first pressure inside the heating chamber 26 and a second pressure outside the heating chamber 26, more particularly inside the intermediate chamber 34. The pressure measurements make it possible to secure that the catalyst 38 operates within the mass flow range where the above formula is valid. Additionally, the device 36 comprises processing means 50, connected to the thermometers 46 and the pressure sensors 48, for determining, by the formula above, based on the temperature difference δT between the first and the second temperature and the pressure difference δp between the first and the second pressure, the concentration of hydrogen peroxide c _Hiθ2 inside the heating chamber.

As discussed above, all of the hydrogen peroxide entering the catalyst 38 is not necessarily decomposed therein. In fact, it is desirable to have an incomplete peroxide decomposition in order to guarantee the linear relationship above. This means that the catalyst 38 can be made comparatively small. If the catalyst 38 was large enough to guarantee complete peroxide decomposition, there would be a risk of complete decomposition already at an intermediate part of the catalyst means which would result in no heat generation at the end of the catalyst 38. Even though the heat loss of the catalyst is very small, it is, nevertheless, present and would result in a temperature drop between the point of complete decomposition and the outlet of the catalyst 38 which would affect the concentration determination. Anyhow, an incomplete decomposition means that hydrogen peroxide will be passed, not only through the exit opening 30 of the heating chamber 26, but also through the catalyst 38, to the intermediate chamber 34. For obvious reasons, it is not desirable to release gaseous hydrogen peroxide into the open. For this reason, an outlet pipe 52 of the intermediate chamber 34 is connected to a main catalyst 54 (schematically illustrated) for hydrogen peroxide decomposition prior to discharge. The gas mixture inside the intermediate chamber 34 is driven through the outlet pipe 52 and the main catalyst 54 by a higher pressure being maintained inside the intermediate chamber 34 than out in the open. The main catalyst 54 is a larger version of the catalyst 38 and will not be further described herein.

In figure 2, a machine 56 working in accordance with a predetermined process for producing packages from a tube of packaging laminate is shown. The machine 56 is, in most aspects, identical to the machine shown in figure 1 and described above. Below, as far as possible, only the parts of the machine 56 differing from the corresponding parts of the machine 10 will be described.

The machine 56 comprises a heating chamber 58 through which a web 60 of packaging laminate is directed, by means of directing rollers 62, 64, for hydrogen peroxide removal by evaporation. The heating chamber 58 has a heating arrangement 66 for effecting the evaporation and a device 68 for determining the concentration of hydrogen peroxide in the gas mixture inside the heating chamber 58. The device 68 comprises a catalyst 70 of the same type as the catalyst 38 described above. The catalyst 70 is surrounded by an insulated housing 72, e.g. made of a mixture of glass and Teflon®, foamed silicone or foamed Teflon® or similar, having poor heat conductivity both in the radial direction and the longitudinal direction of the housing. As apparent from the figures, the catalyst and, thus, the insulated housing, are arranged essentially vertically in figure 1 and

essentially horizontally in figure 2. Both arrangements work equally well and can be chosen in dependence upon the physical properties of the rest of the machine. The catalyst 70 and the insulating housing 72 are arranged inside the heating chamber 58. The housing 72 has an outlet 74 which is connected to a pipe 76 of preferably stainless steel leading out of the heating chamber 58 such that an outlet 78 of the catalyst 70 is directly connected to the outside of the heating chamber, whereas an inlet 80 of the catalyst 70 is directly connected to the inside of the heating chamber 58. The machine 56 further comprises an intermediate chamber 82 similar to the intermediate chamber 34 of the above described machine 10. The pipe 76 leads through the intermediate chamber 82 and well into an outlet pipe 84 of the same.

Just as described above, the gas mixture inside the heating chamber is forced through, not only the housing 72 and the catalyst 70, but also an exit opening 86 of the heating chamber 58. The hydrogen peroxide in the gas mixture is, at least partly, decomposed into water and oxygen inside the catalyst 70, whereby heat is generated causing a temperature rise therein. Further, as discussed above, there is a pressure drop across the housing 72.

If the temperature rise in the catalyst 70 and the pressure drop across the housing 72 are known, the concentration of hydrogen peroxide in the gas mixture inside the heating chamber 58 can be readily calculated by the above formula. In accordance therewith, the device 68 further comprises thermometers 88 for measuring a first temperature inside the housing at the inlet 80 of the catalyst 70 and a second temperature inside the housing at the outlet 78 of the catalyst 70, and pressure sensors 90 for measuring a first pressure inside and a second pressure outside the heating chamber 58. In order to obtain an increased pressure difference between the first and the second pressures, and, thus, in the end, a better accuracy of the concentration calculation, the pipe 76 can be located in the outlet pipe 84 of the intermediate chamber 82, and the second pressure is hence measured inside said outlet pipe 84 of the intermediate chamber 82 at an outlet 92 of the pipe 76.

In figure 3, a machine 94 working in accordance with a predetermined process for producing packages from a tube of packaging laminate is shown. The machine 94 is, in most aspects, identical to the machine shown in figure 1 and described above. Below, as far as possible, only the parts of the machine 94 differing from the corresponding parts of the machine 10 will be described.

The machine 94 comprises a heating chamber 96, in turn, having a device 98 for determining the concentration of hydrogen peroxide in the gas mixture inside the heating chamber 96. The device 98 comprises a catalyst 100 in the form of a

body of ceramic material dipped in precious metal solution. The body has the shape of a circular thick-walled tube. Channels running side by side in the radial direction of this tube fill up the entire interior of its thick wall. The catalyst 100 is surrounded by a cylindrical casing 102 having insulating ends 104, 106, or being covered with insulation, e.g. made of a mixture of glass and Teflon®, foamed silicone, foamed Teflon® or similar, and a jacket 108, preferably made of perforated stainless steel. The catalyst 100 and the casing 102 are arranged inside the heating chamber 96, as illustrated in figure 3. The end 104 of the casing has an outlet 110 for gas mixture outflow whereas the perforations of the jacket 108 of the casing provide for the gas mixture inflow. The outlet 110 coincides with an opening between the heating chamber 96 an intermediate chamber 112 so that an outlet 114 of the catalyst 100 is directly connected to the intermediate chamber 112, whereas an inlet 116 of the catalyst 100 is directly connected to the inside of the heating chamber 96. In this case, the outlet 114 of the catalyst 100 corresponds to the inner wall of the thick-walled tube whereas the inlet 116 corresponds to the outer wall of the thick-walled tube.

The gas mixture inside the heating chamber 96 is forced through the casing 102 and the catalyst 100 wherein the hydrogen peroxide, at least partly, is decomposed into water and oxygen. By measuring the resulting temperature rise together with the pressure difference between the heating chamber 96 and the intermediate chamber 112, the hydrogen peroxide concentration inside the heating chamber can be determined by means of the formula above. As apparent from the figures, the points for measuring the pressure are the same in figure 3 as in figure 1 , whereas one of the points for measuring the temperature differs. In figure 3, one temperature is measured at the outlet 114 of the catalyst 100, more particularly at the outlet 110 of the casing 102, whereas the other temperature is measured outside the casing 102. However, in a state of equilibrium, the temperature outside the casing should be essentially equal to the temperature between the casing and the catalyst 100 at the inlet 116 thereof. In figure 4, a machine 120 working in accordance with a predetermined process for producing packages from a tube of packaging laminate is shown. The machine 120 is, in most aspects, identical to the machine shown in figure 1 and described above. Below, as far as possible, only the parts of the machine 120 differing from the corresponding parts of the machine 10 will be described. The machine 120 comprises a heating chamber 121 , in turn, having a device

122 for determining the concentration of hydrogen peroxide in the gas mixture inside the heating chamber 121. The device 122 comprises a catalyst 125 in the form of a body of ceramic material dipped in precious metal solution. The catalytic

arrangement 200 of the catalytic body 212 and housing 211 is shown in more detail in figures 5 and 6. Thermometers are connected to the device 122 for measuring the temperature at different locations along the device 122, and the pressure may be measured at an inlet 201 and an outlet 202 of the arrangement 200, as can be seen in figures 4 and 5. The heating arrangement 123 is still arranged to supply sterile air into the heating chamber 121 (as in earlier embodiments), and for maintaining a higher pressure inside the heating chamber 121 than in an intermediate chamber 124. This pressure difference is provided for driving a flow of gaseous hydrogen peroxide and air through the catalyst 125, 212, and through the object exit opening 30, 86.

As can be seen in figures 5 and 6, the catalytic arrangement 200 comprises a housing 211 having an inlet 201 and an outlet 202. The housing 211 is made up of a lower body 211b and a lid 211 a, which are interconnected with screws or similar fasteners. The housing is supplied with a heat-insulating material 210, such as a mixture of glass and Teflon®, foamed Teflon® or foamed silicone. The housing can also be formed from said heat-insulating material. In the embodiment shown in figure 6, the insulation is formed as plates, an upper plate 210a, a lower plate 210 b and side plates 210c, d. The housing 211 is formed with an outlet opening, which in the shown embodiment is provided in a lower part of the lower body 211 b. A separate outlet pipe 217 can be connected to the outlet opening. The catalytic arrangement 200 further comprises a catalyst 212, having a ceramic body which is at least partly coated with e.g. a precious metal such as platinum, or any similar metal having catalytic properties for the breakdown of hydrogen peroxide. A permeable element 213 is arranged further downstream of the catalyst 212, and is fitted with a heater 214. This heater 214 is in the shown embodiment electrical, and is powered through the wiring 215, but can be any type of controllable heating element. Thermometers are arranged at the inlet 201 of the catalytic arrangement 200, at an intermediate region 216, in the permeable element 213 and downstream of the permeable element 213, for measuring the temperatures T ₁ , T ₂ , T ₃ and T ₄ respectively.

The pressure difference between the inlet 201 and the outlet 202 of the catalytic arrangement 200, which is created and maintained by the heating arrangement 123, drives the flow through the catalytic arrangement 200. The hydrogen peroxide concentration c of the gas flowing through the catalytic arrangement 200 can be calculated from the following formula: c -T _λ ) (Eq. 1 )

where A, B and C are constants that are found through experiments. The mass flow can be calculated from the formula

*= J ² _{r )} (Eq- 2)

In Eq. 2, the heat Q added to the permeable element 213 must be measured, and this can be done in various ways, e.g. by monitoring an electrical current that is supplied to an electrical heater 214. Another way of estimating the mass flow is through the following formula: m = A _λ -T _λ + A ₂ -T ₂ + A ₃ -T ₃ +A ₄ T ₄

If the temperature 7 ₃ of the permeable element 213 is kept constant, the above expression can be rewritten

Th = A _x -T ₁ + A ₂ -T ₂ +A ₄ -T ₄ + C (Eq. 3) and the parameters Ai, A _∑ and A ₄ as well as C can be determined through experiments. When all parameters and constants are derived, through experiments and/or calibrations, the mass flow m in the catalytic arrangement 200 can be calculated through Eq. 3, and the concentration c is calculated by inserting the value of the mass flow m into Eq. 1.

In equations 1 to 3, the temperature measurements in the catalytic arrangement are used for determining the mass flow therethrough. It is, however, possible to use a pressure difference over the inlet and outlet of the catalytic arrangement for calculations of the mass flow therethrough, as is described for the first embodiment of the present invention.

The above-described embodiments should only be seen as examples. A person skilled in the art realizes that the embodiments discussed can be modified and varied in a number of ways without deviating from the inventive conception. As an example, the invention is not limited to sterilization by means of a bath containing hydrogen peroxide but could also be used in connection with other techniques for hydrogen peroxide application, such as gassing, condensing or spraying.

Further, sterilization of a continuous web of packaging laminate, with im- proved control of the hydrogen peroxide concentration in the heating chamber, has been described above. Naturally, the invention is equally applicable for sterilization of partly formed packages, such as carton-bottles with an open end as initially described or plastic bottles of different kinds, with improved control of the hydrogen peroxide concentration in the gassing chamber. In such an embodi- ment, the gassing chamber should preferably comprise conveying means, such

as a conveyor belt, for conveying the partly formed packages through the gassing chamber.

A thermometer as stated in the application can be any device which is used for measuring a temperature, such as a thermocouple, a thermistor, a bi-metal thermometer, an electrical resistance thermometer, an infrared thermometer etc.

Naturally, the invention could be used in connection with any suitable sterilization agent, hydrogen peroxide just being one example. In the same way, the catalyst could be made of any suitable materials depending on the sterilization agent used and have any suitable design, the above compositions and constructions just being examples. Of course, this is also true for the housing, which can be constructed in a large number of different ways. As an example, a tubular insulating housing could be made of two concentric plastic tubes of different diameters arranged with an intermediate air gap.

It should be stressed that a description of details not relevant to the invention has been omitted and that the figures are not drawn according to scale.

Further, it should be pointed out that the term packaging material as used herein is a generic term for all the matter required to form a specific package, for example packaging laminate, plastic top, etc.